Maybe this app is old news but a search here turned up nothing....
Was at the track (the twisty kind) a few weeks ago, and wanted to get some lap times so I downloaded an app for my android phone called "Trackmaster" http://trackmaster.trackaroo.com/welcome It was $9 and frankly, I wasn't expecting much.

I set it up and threw my phone in the dash clip. All I can say is wow! worth every cent. Lap times, GPS recording of the line, braking points, split times, G-force, you name it. It has a race display mode which shows lap numbers, current time, previous lap, Etc. in real time.
You can export data to excel and to Google earth:
http://dl.dropbox.com/u/23138954/NHI...326PM-1LAP.kmz
http://dl.dropbox.com/u/23138954/NHI...-12%20LAPS.kmz

If you don't have GE installed, here is the screenshot:


As you can see, the accuracy of the recorded line is limited to the refresh rate of the phones on board GPS, with the car roof above it. (my line wasn't that erratic ) The app will accept a Bluetooth GPS with a 5 or 10Hz refresh rate. I think my on board GPS is only 1 or 2Hz, you cover a lot of ground in one second at 100MPH. With the Bluetooth GPS, the line should be a lot more accurate, however for nine bucks, I'm pleased.

 

Interesting, thanks for posting

 

Forgot to mention, the app also has drag race mode and rally mode (non lapping, point to point). I have not tried these modes yet.

Also, on the Google Earth view, there is a datapoint layer, if you turn it on, you will see points around the track where data was recorded (accel/decel, lateral G, speed, elapsed time, etc.) Clicking one of these will give you your data at that point.

You have to play with the pre & post time sliders in GE to see everything.